I've done the update, here is how I done it:
I've downloaded the latest Zend Optimizer: http://www.zend.com/free_download/optimizerThen installed.
First question:
Where should it install:
"c:\Program Files\xampp\php\zendOptimizer"
Secod question:
Wich type of web server do you have:
Apache2
Third question:
Where is your ServerRoot
"c:\Program Files\xampp\apache"
Last question:
Where is your php.ini
"c:\Program Files\xampp\apache\bin"
Then you have to stop, then start the apache from xampp Control panel.

in your php.ini the next changes will apply:
zend_extension_manager.optimizer_ts = "C:\Program Files\xampp\php\zendOptimizer\lib\Optimizer"
will be replaced with:
zend_extension_manager.optimizer_ts="C:\Program Files\xampp\php\zendOptimizer\lib\Optimizer-3.2.6"